A square-shaped complementary split ring resonator (CSRR) filtering structure for isolation improvement is presented in this paper. The proposed research work investigates the design and development of a simple and compact CSRR structure. In order to verify the performance of the proposed filtering element and improve the isolation among the closely placed antenna elements, arrays of configured CSRR structures are implemented between two antenna elements. An array of configured CSRR elements has been integrated with the printed antenna on the top and bottom layers. The proposed filtering elements offer an enhancement in isolation by 25 dB as compared to the simple array. The entire configuration has been simulated using the Ansoft HFSS simulator. Finally, the proposed design is fabricated and experimentally validated. In the experiment, coupling suppression of -51 dB at the operating frequency is successfully achieved, resulting in a recovery of the array pattern. The proposed antenna is highly efficient, which is suitable to be utilized for 5G communication.

This article studies the spatial domain and polarization domain characteristics of multipath channels in a subway-like tunnel environment. Experiments were performed by rotating a horn antenna with 30^◦ half power beamwidth (HPBW) in the azimuthal direction for two different transmitter-receiver (Tx-Rx) distances. The time domain measurement is conducted when carrier frequency is set as 1.8 GHz. The cross-polarization discrimination (XPD) is studied, and it is found that the maximum depolarized signals are from sidewalls. The characteristics of power azimuth spectrum (PAS) of co-polarized and cross-polarized signals follow a multi-cluster Gaussian distribution. Ray-tracing method is employed to investigate the wave propagation in the tunnel environment. The results demonstrate that the main multipath components (MPCs) are around the line-of-sight (LOS) direction, and the reflected waves are from the other end of the tunnel (RWET). The correlation coefficient of co-polarized configuration pursues an increasing function with respect to the Tx-Rx distance and a decreasing function with respect to the cross-polarized configuration.

A compact size (20×21 mm²) planar tri-band electrically small antenna is presented for Wireless ISM, RFID application resonating at 1.57 GHz, 2.47 GHz and 926 MHz. The Proposed structure consists of a dual-slot radiating patch and two split ring structures made using combination of L and U shapes forming a defected ground structure (DGS). Length and width of the planar slot is optimized to get the required frequency bands whereas incorporation of DGS leads to increase in impedance bandwidth. The simulated and measured return losses (S₁₁) of all three frequency bands are greater than 10 dB. Impedance bandwidths of 20 MHz (913-934 MHz), 90 MHz (1.5-1.59 GHz) and 70 MHz (2.43-2.50 GHz) are achieved for the proposed range. The electrically small antenna radiation pattern is omnidirectional, and gains of 0.32 dBi, 1.2 dBi and 1.5 dBi are achieved which makes the antenna suitable for RFID, GPS and WLAN applications.

Compact size microstrip low-pass filters with sharp cutoff characteristics, narrow passband, low insertion loss, high attenuation in stopband, and low cost are highly required in modern wireless communication systems. They are used to suppress the unwanted harmonics and noise caused by Radio Frequency (RF) front ends. In this paper, a new design for compact microstrip LPF is proposed. It is based on utilization of Stepped Impedance Resonators (SIR), Defected Microstrip Structure (DMS), Dumbbell-shaped Defected Ground Structure (DB-DGS), and surface mount capacitor. The filter is realized on an F4B-2 substrate with ε_r=2.65, thickness h=0.5 mm and loss tangent δ=0.0013. The design is carried out using CST-Microwave Studio software. The equivalent circuit of the filter is analyzed and presented using ADS2006A software. The filter exhibits sharp cutoff frequency f_c=1.7654 GHz, wide stopband from 1.7654 GHz to 7 GHz with |S₂₁| less than -10 dB, insertion loss less than 0.15 dB in passband, and reduced size compared to the traditional LPF.

Deep sub-wavelength metamaterials for a wireless power transfer system (WPT) is still a challenge in design and optimization. We propose a large capacitor spiral metamaterial (LCSM) which involves inherent advantages of low operating frequencies and compact structures. The ratio of electromagnetic wavelength to the metamaterial scale can easily reach 1000 at the operation frequency of several megahertz. A hybrid search method, which combines a modified simulated annealing algorithm and a differential evolution algorithm, is applied to the accurate and automatic design of LCSM. The permeability of LCSM is evaluated by finite element analysis and then verified by experimental results. Finally, a small-size WPT system working at 6.78 MHz was constructed to evaluate LCSM. The results show that LCSM can enhance the transfer efficiency of the WPT system from 5.54% to 22.40% at a transmission distance of 15 cm.

A novel ultra-wideband CPW to CPS transition for TSA in landmine detection by GPR system is proposed. The structure is constructed on a 140x140 mm² FR4 dielectric substrate. It is composed of 2 sections. The first is nonuniform tapered asymmetric coplanar waveguide (TACPW), and the second section is nonuniform Tapered Asymmetric Coplanar Strips (TACPS). Electromagnetic Band Gap (EBG) structure of coplanar circular patches exists near the transition open slot and aligned with the outer edge of the CPW ground to act as a capacitive loading. The design of the proposed transition is given in very simple four design steps. The CPW to CPS transition is analyzed theoretically and experimentally. To characterize this transition, back to back transition is constructed; besides, the equivalent-circuit model that consists of nonuniform transmission lines is established. The equivalent circuit is constructed by dividing both sections TACPW and TACPS into 35 sections and using ABCD parameters to characterize each section, and conversion to S-parameters is done using MATLAB Program. The selection criterion of the section length is to maintain a linear change in the characteristic impedance with the distance. The results based on equivalent-circuit model, CST simulation (CST studio ver.15), and measurements are compared. Several parameters are studied through simulations and experiments which are used to derive some design guidelines. The operational bandwidth for the CPW to CPS transition covers from 0 (DC) to almost 10 GHz with minimum return loss reaches -50 dB. For the GPR application (landmine detection) which extends from 0.4 to 3 GHz, the insertion loss of the proposed transition reaches almost -0.5 dB which satisfies the design requirements. The back to back transition performance was simulated and measured. Good agreement is found between numerical and experimental results especially for the GPR ranges of frequencies. The proposed transition has the advantages of compact size, ultra-wide bandwidth, and straightforward design procedure.

Inertial properties of the TE-waveguide modal fields are studied in time-domain making use of an analytical method, named as evolutionary approach to electrodynamics (EAE). To achieve inertial characteristics, electric field vector with dimension of volt per meter and magnetic field vector with dimension of ampere per meter in Maxwell's equations are factorized in SI units to obtain new electric and magnetic field vectors with their common dimensions of inverse meter. Having the fields with the common dimensions makes them summable. Using EAE, modal basis elements that depend on transverse coordinates and modal amplitudes that depend on time and longitudinal coordinate are obtained by solving the boundary eigenvalue problem. As a result of using the new electric and magnetic field vectors, the energetic properties are derived as real-valued functions of coordinates and time. Then, the inertial properties (that is, electromagnetic mass and momentum) of the TE-waveguide modes are obtained as the functions of time.

This work provides an in-depth study on a linear antenna array that consists of 32 elements of CRLH unit cells, and the main radiating beam can be controlled by changing the capacitance of the varicap diode that was designed and simulated with Advanced Design System (ADS 2014) software. ADS software was selected because of its flexibility in accommodating complex design equations. Results show that the main beam can be steered up to 50 degrees from the direction of maximum radiation by changing the capacitances. The main beam gain of the antenna array at boresight of 12 dB has been achieved with an impedance bandwidth of 3 GHz at 10 dB gain threshold. The antenna array performance was analysed in the mmWave frequency range at centre frequency of 28 GHz making it suitable for the upcoming 5G applications. The mmWave path losses were handled by increasing the gain of the antenna array and steering the main lobe over 50 degrees to balance the gain coverage trade-off. The direction of the main beam is controlled by changing the varicap capacitance accordingly.

Magnetic field intensity is modeled using Laplacian equations to study the spatial distribution of magnetic field under spherical shell plasma. The influences of different internal and external radii are also considered. In addition, the magnetic field calculation of plasma space is analyzed. The main conclusions are as follows. The external uniform magnetic field H₀ is the scalar magnetic bit, and the magnetic charge of the shell of the plasma is equivalent to that of a magnetic dipole. The magnetic field in the spherical shell is a super position of a uniform field and a magnetic dipole field. The uniform field is composed of an externally applied uniform field H₀ and a uniform field generated by the magnetic charge on the outer surface of the ball. The magnetic dipole field is generated by the magnetic charge on the inner surface of the shell, and the inside of the shell is a uniform magnetic field. When μ₂/μ₁ is high and a/b is low, the ratio of the magnetic field strength H₃ (the regionis r<a) to the magnetic field strength H₀ (the region is r>b) is low. By contrast, when μ₂/μ₁ and a/b are high, the ratio of the magnetic field strength H₃ to the magnetic field strength H₀ is high. When the magnetic permeability of the inner object is small and the spherical shell is thick, the produced plasma sheath is thick, and the external magnetic field in the spherical shell is weak. Therefore, when the shielding effect is good, the possibility that the ``black barrier'' phenomenon will occur is high, and ground radar detection will be difficult.

This paper concerns the analysis of the performance of a Composite Right-/Left-Handed (CRLH) distributed oscillator. In order to increase its output power, a modification of the standard configuration is proposed. The basic idea is to combine the signals from the two output ports of the structure by means of a Wilkinson combiner, so obtaining a single output generator. The power performance of the conventional two output oscillator and the power performance of the new configuration are numerically compared by changing the number of employed transistors. The same procedure is adopted to analyze the amplitude of the higher order harmonics in the generated signals as a function of the number of active elements. On the basis of simulated data an increase of the output power, together with a second harmonic reduction, is expected for the single output oscillator with respect to the standard CRLH topology. Experimental results fully confirm these numerical predictions.

The effect of users on the efficiency of mobile terminal antennas at 15 GHz, 28 GHz and 60 GHz is studied in this paper. It is performed using three four-element planar arrays. The first operates at 15 GHz with a bandwidth of 0.74 GHz, the second at 28 GHz with a bandwidth of 2.5 GHz and finally the third antenna at 60 GHz with bandwidth of 12.5 GHz. The effect of a user's finger is studied when being placed on four different locations over each antenna element, with six distances between the antenna and user's finger. The losses due to the increased shadowing are studied in terms of radiation efficiency (RE), matching efficiency (ME) and two additional multiple-input-multiple-output (MIMO) parameters i.e., envelop correlation coefficient (ECC) and multiplexing efficiency (MUX). For antennas operating at 28 and 60 GHz, the minimum frequency shift is observed when the finger is placed at 1.5 mm distance from the antenna, whereas for 15 GHz, the minimum resonance shift is observed when the finger is at 2 mm distance. Losses of up to 80% and 70% are observed for RE and MUX, respectively, when the finger is placed at 0 mm for all antennas compared to the case without user (WU). Finally, it is observed that the ME and envelop correlation coefficient losses are insignificant regardless of the antenna and finger variation.

This paper presents a theoretical approach to compare the performance of a directive and a quasi-omnidirectional on-body antennas.Two canonical antennas, namely, a dipole and a rectangular aperture, are considered in the 60 GHz band. We first demonstrate that for this on-body configuration, the classically-defined far-field antenna gain depends on the observation distance. Consequently, we derive results in terms of radiation efficiency and link budget. To do so, the antenna input impedance computation is a preliminary step to normalize the input power to allow a fair comparison between the two antennas. The impedance over a lossy half-plane of an aperture illuminated by a TE10 mode normally polarized is therefore derived into a convenient easy-to-compute formulation, which to authors' best knowledge, is not available in the literature. In terms of link budget, it is obtained that the received power due to an aperture is generally higher than the one due to the dipole in the main lobe direction. A constant difference is observed along the distance, and this difference increases with the aperture width for antennas touching the body. Besides, it is shown that the standard aperture waveguide WR15 exhibits a slightly higher efficiency than a vertical dipole with the same vertical size when being placed at a distance less than 3 mm (i.e., 0.6λ) from the body phantom surface. Above this distance, the dipole and the aperture exhibit similar efficiency in the order of 60%.

This paper devises a framework of phased array antennas to radiate multiple beams for a fixed coverage. The phased antenna array is chosen so that the beamforming can be fixed in selected coverage area. The antenna arrays are employed with a Butler matrix (BM) to form required phases of excitation coefficients to the radiating elements. Optimally designed 4×4 or 8×8 Butler matrix is utilized at the I/O ports of the phased antenna array. The grating lobes are reduced by using the principle of orthogonality to the feeds of subarray (group of column arrays of phased array). This article also exploits the concept of skirt elements to reach the desired coverage area while reducing the beam overlapping in the restricted area. Simulation studies highlight the proposed claims with elaborated numerical analysis of different case studies.

This paper presents two novel bandpass filters using sixteenth mode substrate integrated waveguide (SMSIW) and thirty-second mode SIW (TMSIW) cavities, respectively. The overall size of SMSIW and TMSIW cavities can be reduced by a factor of 15/16 and 31/32 in comparison to the filters designed in the conventional SIW resonator, while keeping almost the same resonant frequency. Based on SMSIW cavity, a first-order filter with the center frequency of 2.45GHz and a transmission zero (TZ) located at the upper-stopband is proposed. The second-order TMSIW cavity filter exhibits one TZ at the lower-stopband and two TZs at the upper-stopband, and it has a better performance of the passband than the former with the same size and center frequency. It also has a wider upper-stopband with suppression of an unwanted harmonic at 7.6GHz. Two intersecting rectangular slots are etched between the two cavities with a smaller angle between them of 30 degrees. The whole size of the filter is 24.2 mm×29.1 mm×0.508 mm. The filters are fabricated in SIW technology, and the frequency response shows good agreement between simulated and measured results.

In recent years, wireless indoor positioning systems have attracted significant research interest. However, maximizing system precision remains challenging, especially for three-dimensional (3D) estimates. In this paper, a novel hybrid approach to resolving this problem is proposed through the development of a multiagent system composed of a Bayesian network and a deep neural network for 3D indoor positioning. The proposed system is based on a combination of the multilateration and fingerprint methods in order to reduce the acquisition region of the received signal strength vectors. In addition, the relationship between the quality of the received signal and the noise level, which is influenced by the increase in the number of access points and the number of persons moving within the environment, is considered by the system. The proposed approach exhibits a better performance than other algorithms with an average positioning error of less than 0.9 m. This result represents a difference of more than 22 cm with respect to the most similar algorithm.

Electromagnetic band gap (EBG) structures offer unique solutions for effectively manipulating electromagnetic waves over a broad range of frequencies for a wide range of applications. However, most EBG designs reported so far either require sophisticated fabrication processes or have limited tunability and reconfigurability. In this paper, we investigate the potential to implement high performance tunable and reconfigurable EBG components using a novel optical control approach. This technology allows the generation of EBG structures through spatially-resolved photogeneration of free carriers in a semiconductor, without any complex fabrication processes. As a prototype demonstration, a reconfigurable microwave frequency tunable band-stop filter (BSF) based on photo-induced uniplanar EBG structures has been investigated through simulation. In this approach, the required EBG patterns are directly illuminated onto a Ge ground plane mounted to the bottom of a Duroid substrate for tunability using a digital light processing (DLP) projector. On the basis of HFSS simulations, the bandwidth of the BSF can be tuned by modifying the EBG pattern filling factor. The center frequency of the BSF could also be tuned from 8-12 GHz by adjusting the period of the EBG structure. In addition, two limiting factors, i.e., localized heating effects and finite lateral spatial resolution (due to carrier diffusion), that may affect the circuit performance in this technology have been investigated and discussed. By using a mesa-array structured ground plane, this approach is promising for developing tunable and reconfigurable circuits such as filters from the microwave to terahertz regimes.

Design and analysis of a novel wide-band covering, hetero triangle linked hybrid web fractal antenna is presented in this paper. The hetero triangle linked hybrid web structure has been designed through multiple iterations in the CST MICROWAVE STUDIO electromagnetic simulation tool and has been fabricated on FR4 dielectric of ε_r = 4.4 with height of 1.6 mm. The proposed antenna offers a comprehensive bandwidth of 18.055 GHz, covering from 1.945 GHz to 20 GHz. It supports various applications starting from 3G, LTE, ISM, Bluetooth, Wi-Fi, WLAN (2.4-2.48 GHz) and 5.2/5.8 GHz (5.15-5.35 GHz/5.72-5.82 GHz), WiMAX operating in the 2.3/2.5 GHz (2.305-2.36 GHz/2.5-2.69 GHz), 5.5 GHz (5.25-5.85 GHz) and Satellite communication (Ku band: Uplink of 14 GHz and Downlink of 10.9-12.75 GHz). The proposed antenna provides peak realized gain of 7.17 dB with efficiency more than 78% in the operating band. The antenna parameters such as reflection coefficient, gain and radiation patterns are determined through numerical simulation, and good matching is obtained with measured results.

A one-shot rescaling process, namely Automated Scaling Region of Interest (AS-ROI), is combined with an inversion technique of Forward-Backward Time-Stepping (FBTS). The purpose is to alleviate the ill-posedness and nonlinearity of inverse problem by reducing the size of the unknown problem. The inversion solution is carried out to reconstruct tumour as an unknown object in coarse investigation domain of lung area which is then rescaled down corresponding to object location and size. In this paper, edge preserving methods consisting of edge preserving regularization and anisotropic diffusion are imposed alternately on the solution and reconstructed profiles to improve the current method of AS-ROI. Results on the reconstructed lungs and tumours give significant insight of the proposed work. Accuracy level for the reconstructed profiles are significantly improved in spite that spatial resolution is retained as the original setting of FBTS.

Research on RCS evaluation for electrically large objects has been a hot topic for decades. Although multilevel fast multipole algorithm (MLFMA) has been the most popular method in scattering computation, due to the limitation of both CPU speed and memory size in a single computer, realistic large targets require discretization with millions of unknowns still cannot be solved by sequential implementations of MLFMA. In this paper, we introduce a Docker-enabled parallel MLFMA computing system based on MPI, which is proved to be friendly for deployment and economical for scalability, to solve electrically large scattering problems. In addition, the capability of the proposed system has been demonstrated by several canonical examples.

In this work, the design of a switched beam antenna array based on an optimized Butler matrix feeding network was done with a compact microstrip structure and a set of microchip antennas working at 2.45 GHz. The obtained antenna feeding network was tuned and optimized by using suitable unsupervised techniques to obtain a compact and efficient structure. A microstrip antenna array prototype composed by four elements was fabricated and experimentally tested. Good impedance matching and radiation properties have been experimentally verified with reference to the main beam steering capability.